Fertilizer is made from phosphoric acid liquor, which incidentally contains significant amounts of uranium, typically about 0.2 g/1. In order not to waste the valuable uranium, a process has been developed by Oak Ridge National Laboratories to separate it from the acidic liquor which is contaminated with metal ions, principally iron in a typical amount of about 12 g/1. (See the article in I&EC Process Design and Development, Vol. II, page 122, January 1972 by F. J. Hurst, D. J. Crouse, and K. B. Brown titled "Recovery of Uranium from Wet-Process Phosphoric Acid. " The same process is described in more detail by F. J. Hurst et al. in ORNL-TM-2522 Report entitled "Solvent Extraction of Uranium from Wet-Process Phosphoric Acid, " April 1969. Also, see U.S., AEC Report ORNL 2952, June 30, 1960 by F. J. Hurst and D. J. Crouse titled "Recovery of Uranium from D2EHPA Extractant with (NH.sub.4).sub.2 CO.sub.3."
This prior process is divided into two extraction cycles. In the first cycle the uranyl ion (UO.sub.2 .sup..sup.+2) and some ferric ion is extracted using di-2-ethylhexyl phosphoric acid (D2EHPA) and tri-n-octyl phosphine oxide (TOPO) in kerosene, the uranyl ion forming a complex with the D2EHPA and TOPO. The solvent is then stripped with a portion of the acid leaving the extractor and containing ferrous ions to produce a more concentrated acidic aqueous stream of ferric ions and U.sup..sup.+4 ions. The U.sup..sup.+4 ion is then oxidized with air to the uranyl ion.
In the second cycle of the prior process the concentrated acidic aqueous stream from the first cycle was again extracted with kerosene containing D2EHPA and TOPO, then stripped with water containing 2 to 2.5 moles/1 (NH.sub.4).sub.2 CO.sub.3 which would precipitate ammonium-uranyl-tricarbonate, (NH.sub.4).sub.4 UO.sub.2 (CO.sub.3).sub.3, (AUT) and some ferric hydrate. The AUT could be recrystallized to purify it.
This process typically produced uranium containing 2 to 4% iron (based on the uranium) before recrystallization and recovered about 94% of the uranium in the feed. Ceramic grade uranium, which is used as fuel in reactors, requires no more than 0.04% iron (based on the uranium). (All percentages herein are by weight unless otherwise indicated.)